AbstractThe invention relates to a laser arrangement, comprising a laser (2) having a laser cavity (20); a least one cavity (30) external to the laser (2) which reflects one part of the light emitted by the laser (2) back into the laser cavity (20); a voltage measuring device (4) for measuring a voltage on an active section (21) of the laser (2), wherein an imbalance of the emission wave length of the laser (2) and/or a property of a material adjacent to the external cavity (30) can be determined. According to the invention, the external cavity (30) comprises an optical waveguide (34) coupled to the laser (2). The invention also relates to a method for controlling a laser and to a measuring method.